A method of making a nonwoven sheet by the melt blowing process has long been acknowledged publicly as disclosed in Japanese Patent Publication No. 22525, 1969, U.S. Pat. No. 3,825,380, for example.
In nonwoven sheet conventionally obtained by the melt blowing process, fibers are insufficiently separated from each other and there exist randomly many rope-like fiber bundles in which the fibers are entangled with each other, which fibers are formed into thick and coarse fiber bundles with resulting irregularity in weight of unit area of said sheet and unevenness in thickness. In addition, uniformity and smoothness of the surface of said sheet are spoiled by polymeric particles having no fibrous configuration, produced during the melt blowing process, and the rope-like fiber bundles having diameters from ten times to hundreds of times the diameter of the fibers constituting the sheet.
On the other hand, there are conventional methods in which merely a cumulative fiber mass is used as a padding for clothes or mats or bedclothes in order to give heat-retaining or heat insulating properties, or in which a synthetic polymeric film with aluminum vacuum evaporated onto it, is used in combination with the above-mentioned method. In the former method, retention of air is inevitably deteriorated to a large extent due to lowered compressive resilience of the fibers. In the latter method, the fibers used generally shrink during dry cleaning because of heat shrinkage of said fiber. Synthetic polymer films have a very coarse touch and when stitched with a needle machine, its tensile strength and tear strength are reduced to a large extent.
In order to eliminate the above-mentioned demerits, a method has been provided in which a nonwoven fabric consisting of filament fibers has a vacuum evaporated metal layer applied to one surface, and is layered with a web composed of short staple fibers on the surface of said metal layer by needle punching. (Japanese Utility Patent Publication No. 50-22150).
This method has a disadvantage, however, that since the unity of said web with said nonwoven fabric composed of filaments done by needle punching, a number of pores penetrating through the sheet in its thicknesswise direction are produced and heat tends to radiate through the pores so that sufficient heat retaining effect cannot be achieved.